F2 rear brake binding

[Magster]

Hello again everybody,

I am in need of some more help if possible. My rear brakes are binding and the disc is heating up and the calipers are stuck solid.
They do ease off if left for some time then it all happens again only whilst riding though.
I have so far removed caliper checked seals and sliders all fine I think so have moved on to master cylinder.
If I push one piston in the other pops out and I can't push them both in at the same time. This leads me to think that it is the master cylinder not letting the pressure back up.
I installed new seals etc in the master cylinder when rebuilding and it seems to operate fine. There does appear to be one hole blocked but I am unsure where, if anywhere it should come out?
I have attached a picture of it hoping someone can help?
Thanks,
Magnus. [ Guests cannot view attachments ]

[Johnwebley]

how old are the seals in the caliper?

 they should be soft and flexible,as they retract the pistons

[Magster]

The seals are new, I did wonder if they were sticking. They push in by hand relatively easily, but I can't push them both back at the same time even with a clamp.
Thanks, Magnus.

[Magster]

Sorry, I just realised I would be causing confusion speaking of 2 pistons in the caliper.
The calpier is from a VF750. I put the twin pot caliper on as suggested on several forums as an upgrade to braking as my caliper was so far gone.
The master cylinder is original but with new seals and piston.
Hope that helps clear things up a bit.
Thanks,
Magnus.

[Mag1]

Have you put the seals in the correct way when rebuilding the master cylinder?, one will be slightly larger than the other, and thicker.  Clean it out also with compressed air if possible.

[Magster]

Hi, I have cleaned it out with compressed air and am pretty sure the seals are the right way around.
The more I dig around on forums it looks like in that blocked cavity there should be a tiny return hole.
I have tried clearing it with pins and guitar strings but it is solid. Have read elswhere that I could drill it with a 0.4mm hole so I think that will be my next effort.
Thanks, Magnus.

[royhall]

Your pistons will struggle to retract with that hole blocked, thats your problem. They do get blocked solid if left for a good time without use. You can clear it with a small drill bit but do it by hand not with a power drill. I usually hold the drill in a vice and gently turn the cylinder by hand. Get that clear and you should be good to go. But do it carefully as the hole is not the same diameter all the way through. It starts quite large the goes down to a tiny hole (hence not using a power drill). If you can clear the large part the small hole will poke through with guitar string wire.

[Magster]

Hi , thanks for that. I have now drilled it (by hand using a pin vice) with a 0.4mm hole and have reassembled the brakes and bled the system down.
I will have to wait for a better day to get out and give it a test run again.

Thanks for all the help,

Cheers, Magnus.